A membrane-type flowmeter having a membrane which effects single reciprocation in association with supply and discharge of a predetermined quantity of fluid to a metering chamber has hitherto been described as a flowmeter for metering a flow rate of a fluid such as a gas or the like (see, e.g., JP-A-2004-93497).
As shown in FIG. 20, such a flowmeter 100 is provided with a membrane section (omitted from the drawings) which effects reciprocation in response to supply and discharge of a gas into and from the metering chamber. A link mechanism 101 is joined to a wing shaft which pivots in association with the reciprocation of the membrane section. The link mechanism 101 is formed by combination of a pair of longer gate hooks 101a and a pair of shorter gate hooks 101b. A pair of magnets 103, which are symmetrical about the center, are provided along a brim of a rotary member 102. A lead switch 104, which is activated when the magnets 103 have been rotated to a specific rotational phase, is provided. Moreover, a controller 105, which determines a flow rate in accordance with a signal output from the lead switch 104 and displays the thus-determined flow rate on a display section 106, is also provided.
The rotary member 102 comprises a crank shaft 102a which is rotatably provided on a support table 107 placed in an upper portion of a casing (omitted from the drawings); and a rotary disk 102b attached to the crank shaft 102a. A crank arm 108 is attached to the crank shaft 102a. The crank arm 108 is equipped with pivotal valves 112 which open or close gas inlet ports 110 and gas outlet ports 111 by way of a pair of crank rods 109, 109.
Accordingly, the rotary disk 102b causes a single rotation when the membrane has effected a single reciprocation in response to supply and discharge of a gas to and from the metering chamber, and hence the pair of magnets 103, 103 attached to the rotary disk 102b also rotate in the same fashion. The lead switch 104 detects rotations of the magnets 103, 103 and sends signals to the controller 105, where the flow rate is computed. The thus-computed flow rate is displayed on the display section 106. The pair of pivotal valves 112 pivot in association with the rotation of the rotary disk 102b, thereby opening and closing the gas inlet ports 110 and the gas outlet ports 111 as appropriate. Thus, the gas is supplied and discharged.